Highest-Paid Actresses 2011

Sampling Imogen Heap's 'Hide and Seek,' the song is a first for up-and-coming R&B singer, whose self-titled debut album dropped in 2010.

Six months ago project creator Adam Young was living in his parents' basement in Owatonna, Minnesota, stuck in a low-paying job. 'Fireflies,' among his other songs, was originally written merely for his own amusement, not necessarily intended to share with others. A song about insomnia, 'Fireflies' features guest vocals by Relient K frontman Matt Thiessen.

The song was produced as a studio experiment, where audio mixer Dr. Luke provided the sample of Dead or Alive's 1984 hit 'You Spin Me Round (Like a Record),' and Flo Rida recorded his own lyrics over the song.

Our seventh top song of 2009 -- toiling between the dysfunctionality of a relationship and the fact that her life is better with him -- now holds the Billboard 100 record for the largest leap to the No. 1 position.

A touching sentiment of fragility, the song was inspired from a falling-out lead vocalist Caleb had a couple years ago with the other band members in Glasgow. The song earned the group their first Top 40 hit, reaching No. 4 on the U.S. Billboard 100, No. 2 on the UK and Australian Singles chart, as well as topping charts in Norway, Germany, Canada, Belgian and other countries in 2009.

The catchy dance number was produced by Will.i.am and French house DJ David Guetta, the latter making an appearance in the music video along with Katy Perry, American rapper Kid Cudi, and model/actress Chantal Jones.

Lady GaGa says she wrote the song as a tribute to her rock 'n' roll boyfriends. Despite its upbeat electropop vibe, the song denotes a darker meaning of not "sex, drugs, and rock 'n' roll" but rather, "sex, gambling, and bisexuality."

2009's third biggest song is about a girl that Iyaz (discovered by reggae-fusion singer and rapper Sean Kingston) can't get out of his head, resulting in an infectious melody that we "can't keep out" as we're "singin' like na na na everyday" while our "iPod's stuck on replay." Thanks dude -- you really got the point across.

Lil Wayne was not originally featured in the song. As president of the record label the album is under, Lil Wayne surprised Sean with a rap verse following the second verse in a demo. Since it's debut June 30, 2009, the single has reached the Top 5 at the Billboard Hot 100 chart, peaking at No. 2 since September.

The first lines of our No.1 top song of 2009 were inspired by Swift overhearing a male friend of hers on the phone with his girlfriend. She was berating him for hanging up on her.